The present invention relates to an electrophotographic image forming apparatus, a color electrophotographic image forming apparatus, a process cartridge process cartridge detachably mountable to such an electrophotographic image forming apparatus, and an electrophotographic photosensitive drum. Here, the electrophotographic image forming apparatus is an apparatus which forms an image on a recording material through an electrophotographic process. The electrophotographic image forming apparatus may be an electrophotographic copying machine, an electrophotographic printer (a LED printer, a laser beam printer or the like), an electrophotographic printer type facsimile machine, an electrophotographic printer type word processor or the like.
The process cartridge is a cartridge containing as a unit an electrophotographic photosensitive drum and process means such as a charge member, a developing member or a cleaning member, the unit being detachably mountable to the main assembly of the image forming apparatus. The process cartridge is a cartridge containing as a unit an electrophotographic photosensitive drum and at least one of process means such as a charge member, a developing member and a cleaning member, the unit being detachably mountable to the main assembly of the image forming apparatus. The process cartridge may contain as a unit an electrophotographic photosensitive drum and at least a developing member, the unit being detachably mountable to a main assembly of the electrophotographic image forming apparatus.
In an electrophotographic image forming apparatus using the electrophotographic image forming process, use has been made with the process cartridge type in which the process cartridge comprises as a unit the electrophotographic photosensitive member and process means actable on the electrophotographic photosensitive member, the unit being detachably mountable to the main assembly of the electrophotographic image forming apparatus. With the use of the process cartridge type, the maintenance operation can be carried out in effect by the users without necessity of relying on serviceman, and therefore, the operativity is improved. Therefore, the process cartridge type is widely used in the field of electrophotographic image forming apparatus. Such a process cartridge is provided at a longitudinal end of the photosensitive drum with a driving force receiving portion. When the process cartridge is mounted to the main assembly of the apparatus, the driving force receiving portion is brought into engagement with a driving force transmitting portion provided in the main assembly of the apparatus. By doing so, the photosensitive drum can receive the rotational driving force from the main assembly of apparatus, and therefore, is rotatable. In the case of a color electrophotographic image forming apparatus, a plurality of process cartridges containing different color developers are mounted. For example, in the case of a full color electrophotographic image forming apparatus, four process cartridges containing a black color developer, a yellow color developer, a magenta color developer and a cyan color developer, respectively. When a plurality of process cartridges are mounted, the following problems may arise.
Referring to FIG. 14, the positional deviation of the process cartridge results in the deviations of the image formation positions in the form of a sunisoidal wave on the recording material (paper, textile or the like).
In FIG. 14, the abscissa represents a distance from a leading end of the image, and the ordinate represents the positional deviation from the correct image formation position.
The causes may be (1) an axis of the drum driving gear provided in the main assembly of image forming apparatus is inclined relative to the gear of the motor, by which the image formation position periodically varies at the regular intervals of the drum driving gear rotation, that is, in the period of rotation of the photosensitive drum: (2) by a non-uniform rotation of the photosensitive drum, the positioned periodically varies at the intervals of the circumferential length of the photosensitive drum.
In order to adjust the phase relation due to the positional deviations among the four color images, as shown in FIG. 14, the image formation start timing for each color is controlled. More particularly, the image formation is carried out for each color, and the image formation positions are detected.
As shown in FIG. 14, when the Bk (black) color is taken as a reference, the Y color (yellow) color is deviated toward the leading end of the image by a distance distance y, by which the relative color misregistration from the Bk color image can be reduced. Similarly, the M (magenta) color image is deviated by a distance m, C (cyan) color image is dictated by a distance c. By such a phase control, the color misregistration can be reduced. However, the phase detection and the control require a certain length of time. Therefore, if these operations are carried out frequently, the image formation time becomes longer. For example, in them describe the structure, the meshing engagement relation between the photosensitive drum and drum driving gear, that is the phase relationship may change in the rotational direction. Therefore, the phase detection and the phase control have to be carried out for each mounting-and-demounting of the process cartridge.
The present invention is directed to a solution to the problem.
Accordingly, it is a principal object of the present invention to provide a process cartridge, an electrophotographic image forming apparatus to which the process cartridge is detachably mountable in which the rotational accuracy of the electrophotographic photosensitive drum is improved.
It is another object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which the engagement position with respect to the rotational direction is made constant when the driving force receiving portion of the process cartridge is brought into engagement with the driving force transmitting portion provided in the main assembly of the image forming apparatus.
It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, in which when the driving force receiving portion of the process cartridge is brought into engagement with the driving force transmitting portion provided in the main assembly of image forming apparatus, the engagement is accomplished at a predetermined position.
It is a further object of the present invention to provide a process cartridge and a color electrophotographic image forming apparatus to which the process cartridge is detachably mountable in which the color misregistration can be suppressed when a color (full-color) image is formed.
It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable in which the phase detection and phase control operations are not required each time the mounting-and-demounting of the process cartridge.
It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable in which there is provided a permitting portion for permitting engagement at a predetermined position in order to make the engaging position constant when a twisted projection and a twisted recess are engaged with each other.
It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, wherein the positional accuracy and the rotational accuracy of the electrophotographic photosensitive drum is improved with a simple driving structure for the electrophotographic photosensitive drum.
It is a further object of the present invention to provide an electrophotographic photosensitive drum suitable for accomplishing the above-described respective objects.
The electrophotographic image forming apparatus may be a monochromatic and color (full-color) electrophotographic image forming apparatus.
The present invention is particularly effective when it is used with a color (full-color) electrophotographic image forming apparatus and a process cartridge for a color (full-color) electrophotographic image forming apparatus.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.